1. Field of the Invention
This invention relates to an anti-friction composition and, more particularly, to a lubricant additive that provides a protective coating to moving metal parts and reduces friction and wear therebetween.
2. Related Art
Friction occurs when two surfaces in relative motion, such as metal machinery component surfaces, contact each other. This friction results in the gradual removal of solid material from the contacting surfaces, i.e., wear. By reducing the friction, wear can be reduced.
More particularly, metals have surface asperities that strike each other when pressed close enough together, especially under extreme pressure, resulting in the "welding" and tearing of the metal surfaces. This wear is known as adhesive wear, scuffing, contact wear, galling or boundary lubrication wear. Many attempts have been made to reduce this wear.
In this regard, it is widely known that lubrication has a profound effect in reducing wear. Lubrication separates the moving surfaces with a film which can be sheared with low resistance, without causing damage to the surfaces. Examples of conventional lubricants follow.
First, a softer metal can be used to coat a harder metallic surface sought to be protected. For example, the introduction of the soft metal lead into a machinery lubricant such as oil has effectively been used for this purpose.
Lead, however, has been shown to combine with sulfur which is often present in the lubricant, and can result in corrosives being formed which then attack the actual metals for which protection is sought. Additionally, lead is extremely toxic and should be avoided.
Second, certain shearable protective substances which adhere physically to the surfaces to be protected, have been used for wear reduction. Under high pressure, part of the protective substance is sheared off and redeposited forward of the sheared section. Molybdenum disulfide is such a substance.
Molybdenum disulfide, however, is not as effective as lead, and cannot endure the same pressures and afford the same protection as lead. This chemical also still results in the base metals' asperities striking each other, so wear will still occur.
Graphite is also such a substance, since it depends upon the shearing action of the graphite crystal. Graphite, however, is even less effective than molybdenum disulfide.
Both graphite and molybdenum disulfide, solid substances, have the further disadvantage that, if used in a very high pressure, slow speed application, they can "pack" a bearing so tightly that seizure of the bearing may occur with much subsequent damage.
Third, a protective coating of polytetrafluoroethylene ("PTFE"), a plastic-like substance sold commercially by DuPont as Teflon.TM., has been used as an oil additive. An example of such a popular commercial product is believed to be Slick 50.TM.. PTFE migrates to the interstices of metal surfaces, providing a physical bond with the machinery metals and a protective layer.
While it is known that wear and friction can be reduced by the introduction of PTFE in liquid lubricants, (see, e.g. U.S. Pat. No. 3,933,656) PTFE is a soft resin that cannot endure very extreme pressures of two metals being pressed together.
Fourth, there also is known the introduction into a lubricant of chemical additives which "contaminate" the metal surface. These additives are intended to prevent or reduce the welding that occurs when the surface asperities come into contact. Sulfur, phosphorus, and chlorine compounds have been used for this purpose.
These compounds, or combinations thereof, perform by chemically reacting with the iron surface of the metal parts to form the respective contaminating compounds, iron chloride, iron phosphide, iron phosphate, iron sulfide, and iron sulfate. It is believed the commercially popular oil additive product Duralube.TM. is a "contaminant" additive, since it appears to be a butyric acid chloride in naphtha, specifically Shell.TM. Sol #140.
Another example of a contaminant additive is Zinc Dialkyl-dithiophosphate ("ZDDP"), which is used as an extreme pressure antiwear additive in gear lubes, wheel bearing greases, etc. ZDDP is available from Elco Corporation in Cleveland, Ohio, and Lubrizol. The sulfur and phosphorus thereof combine with the iron to form a contaminant layer of iron sulfide or sulfate, iron phosphide or phosphate and reduce the welding of the iron on the two rubbing metal surfaces.
The disadvantages with using contaminant chemical additives follow.
In combining with the machinery metal, it is necessary to use or "eat up" part of the metal itself in order to create the protective layer, a self-defeating process. Thus, the above chemicals can only slow wear, not stop it.
Additionally, because of the chemical nature of these protective substances, excessive use can be harmful as corrosive effects can occur.
If a combination of the third and fourth approaches described above is attempted, i.e., PTFE added to these chemically reactive, contaminant-type additives, for added anti-friction properties, the PTFE tends to migrate to the interstices of the machinery metal before the chemical reactions take place. This PTFE coating, which is relatively unreactive, then tends to interfere with the reaction of the contaminant type additives in that they are prevented from reaching the machinery metal surfaces. With enough pressure the PTFE layer is broken through and adhesive wear occurs. The wear can be reduced only when the contaminant type additive is allowed to react with the machinery metal surface and form the contaminant protective layer.
Fifth, it is known to use a mixture of bismuth metal and tin metal to provide wear and friction reduction. U.S. Pat. No. 4,915,856 describes that these metals, as well as others from the group lead, copper, zinc, antimony, aluminum, magnesium, selenium, arsenic, cadmium, tellurium, graphite, and indium, can be mixed in powdered form with an epoxy or polymeric organic carrier and a percentage of oil or grease for lubricating rail car wheels and other external applications of similar nature.
This patent, however, describes that direct application of the modified lubricant to the machinery metal surface is required, which is not practical in many applications, such as liquid petroleum lubricants for gasoline and diesel engines. Prior coating of engine parts before assembly is also not practical as it is labor intensive, time consuming, and the polymeric carrier would be diluted by the usual lubricant of the engine, resulting in the powder/polymeric mixture coating being quickly worn off during operation of the engine and washed away by the action of detergent additive packages usually incorporated in the petroleum lubricants used. Further, the dry lubricant introduced in the form of a powder would be quickly removed by a lubricant filter which is usually present in the machinery. Settlement and the clogging of oil passages is also a problem.
Although the prior art lubrications described above provide some anti-friction benefits, the health, environmental, corrosion, and efficiency drawbacks associated therewith are significant. The prior art, therefor, does not teach an effective, non-corrosive, non-toxic, non-metal reacting anti-friction composition.